Direct Capture of CO2 from Ambient Air using Solid Sorbents

CO2 emissions related to human activities utilizing fossil fuels are generally believed to cause climate changes. Conventional CO2 capture technologies focus on capturing CO2 at large pointed sources, such as power plants. But distributed sources account for around one-third to one-half of the total emissions, which cannot be captured by conventional CO2 capture technologies. Those emissions can be mitigated by one technology – CO2 capture direct from ambient air (DAC), which attracts increasing attention nowadays.
For DAC, a process based on the use of regenerative solid sorbents may be an attractive, energy efficient alternative to the use of aqueous solvents due to a lower specific heat. Among solid sorbents, amine-functionalized sorbents have been identified as promising sorbents for DAC, due to their relatively high CO2 capacities under the air capture conditions and a moderate desorption temperature (100 – 120 °C).
In this thesis, a novel process is developed and experimentally demonstrated, for CO2 capture from ambient air to produce CO2 enriched air to enhance microalgae cultivation. First, an amine functionalized sorbent is selected, initially based on its water and CO2 equilibrium adsorption capacity. Subsequently, the selected sorbent is characterized on its stability under different conditions for a wide range. After selecting the sorbent, a selection of operating conditions for the adsorption step is made, targeting fast sorbent saturation and a low pressure drop. After establishing proper adsorption conditions as well as a suitable adsorber configuration, sorbent desorption is investigated in view of the production of CO2 enriched air for microalgae cultivation. The established process uses a radial flow reactor for CO2 adsorption and a fluidized bed for desorption using air as the sweep gas, with sorbent circulation between adsorber and desorber. This process is evaluated and, based on the operating costs, found to be an economically competitive way to capture CO2 from ambient air for use in microalgae cultivation.